The effect of 5-hydroxytryptamine and molluscan neuropeptides on the hearts of gastropod molluscs: Mechanical activity and second messengers

Abstract

Isolated hearts from the gastropods Melongena corona and Busycon contrarium were exposed to increasing concentrations of the molluscan neuropeptides FMRFamide, FLRFamide, and pQDPFLRFamide. FMRFamide increased the amplitude of contractions of the hearts of both species. The response of hearts from B. contrarium to FLRFamide was similar to that induced by FMRFamide, but hearts from M. corona were less sensitive to excitation by FLRFamide. Hearts from M. corona were excited by pQDPFLRFamide; this heptapeptide had no effect on hearts from B. contrarium. Hearts of both species were excited by APGWamide, but SCP B had no effect on the hearts of either species. Myomodulin inhibits the activity of B. contarium hearts, but is cardioexcitatory in M. corona. Serotonin (5HT) was cardioexcitatory and acetylcholine inhibitory in both species. Agonists of cAMP had no effect on the mechanical activity of the hearts, but phorbol esters excited the hearts of both species. The effects of 5HT and FMRFamide on the levels of second messenger molecules in ventricles from M. corona were examined. Neither 5HT nor FMRFamide caused changes in the levels of cAMP in isolated ventricles from M. corona, but both agents increased the amount of IP 3 in the ventricle.